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Full text of "IS 14674: High Voltage Alternating Current Circuit-breakers-guide for Seismic Qualification of High Voltage Alternating Current Circuit-breakers"

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Disclosure to Promote the Right To Information 

Whereas the Parliament of India has set out to provide a practical regime of right to 
information for citizens to secure access to information under the control of public authorities, 
in order to promote transparency and accountability in the working of every public authority, 
and whereas the attached publication of the Bureau of Indian Standards is of particular interest 
to the public, particularly disadvantaged communities and those engaged in the pursuit of 
education and knowledge, the attached public safety standard is made available to promote the 
timely dissemination of this information in an accurate manner to the public. 



Mazdoor Kisan Shakti Sangathan 
"The Right to Information, The Right to Live" 



Jawaharlal Nehru 
'Step Out From the Old to the New" 



IS 14674 (1999) : High Voltage Alternating Current 
Circuit-breakers-guide for Seismic Qualification of High 
Voltage Alternating Current Circuit-breakers [ETD 8: High 
Voltage Switchgear and Controlgear] 



Satyanarayan Gangaram Pitroda 
Invent a New India Using Knowledge 




5fR TT^ ^TT <sMHI | *ft ^fft ^TRT ^ff ^TT ^T^fT )f 

Bhartrhari — Nltisatakam 
"Knowledge is such a treasure which cannot be stolen" 





BLANK PAGE 




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PROTECTED BY COPYRIGHT 



IS 14674: 1999 
IEC 1166 (1993) 

„ ( Reaffirmed 2004 ) 

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Indian Standard 

HIGH VOLTAGE ALTERNATING CURRENT 

CIRCUIT-BREAKERS— GUIDE FOR SEISMIC 

QUALIFICATION OF HIGH VOLTAGE 

ALTERNATING CURRENT CIRCUIT-BREAKERS 



ICS 29.120.60 



©BIS 1999 

BUREAU OF INDIAN STANDARDS 

MAN A KB HA VAN, 9 BAHADUR SHAH ZAFAR MARG 
NEW DELHI 110002 

June 1999 Price Group 7 



High Voltage Switchgear and Controlgear Sectional Committee, ET 08 



NATIONAL FOREWORD 

This Indian Standard which is identical with IEC 1166 (1993) 'High-voltage alternating current circuit- 
breakers — Guide for seismic qualification of high-voltage alternating current circuit-breakers', issued by 
the International Electrotechnical Commission (IEC), was adopted by the Bureau of Indian Standards on 
the recommendations of the High Voltage Switchgear and Controlgear Sectional Committee (ET 08) and 
approval of the Electrotechnical Division Council. It is a guide that specifies seismic severity levels and 
provides procedures to seismically qualify only those HV alternating current circuit breakers which are 
ground mounted. 

The text of the IEC 1166 (1993) has been approved as suitable for publication as Indian Standard 
without deviations. 

In the adopted standard, certain terminology and conventions are not identical to those used in Indian 
Standards. Attention is specially drawn to the following: 

a) Wherever the words 'International Standard' appear referring to this standard, they should be read 
as Sndian Standard'. 

b) Comma (,) has been used as a decimal marker while in Indian Standards, the current practice is 
to use a point (.) as the decimal marker. 

In this adopted standard, reference appears to certain International Standards for which Indian Standards 
also exit. The corresponding Indian Standards which are to be substituted in their place are listed below 
along with their degree of equivalence for the editions indicated: 



International Standard 



Corresponding 
Indian Standard 



Degree of 
Equivalence 



IEC 50 (441): 1984 
International Electrotechnical 
Vocabulary — Chapter 441 : 
Switchgear, controlgear and 
fuses 



IS 1885 (Part 17): 1979 



Equivalent 



IEC 56 : 1 987 High - voltage 
alternating-current circuit- 
breakers 



IS 13118: 1991 



Identical 



IEC 68-1:1988 
Environmental testing — 
Part 1 : General and guidance 



IS 9000 (Parti): 1988 
& IS 9001 (Parti): 1984 



Equivalent 



IEC 68-2-6:1982 Environmental 
testing — Part 2 : Tests — Test Fc 
and guidance: Vibration 
(sinusoidal) 



IS 9000 (Part 8): 1981 
& IS 9000 (Part 13) :1979 



do 



(Continued on third cover) 



IS 14674 : 1999 
IEC 1166(1993) 

Indian Standard 

HIGH VOLTAGE ALTERNATING CURRENT CIRCUIT-BREAKERS - 

GUIDE FOR SEISMIC QUALIFICATION OF HIGH-VOLTAGE 

ALTERNATING CURRENT CIRCUIT-BREAKERS 

1 Scope and object 

This International Standard applies only to ground mounted high-voltage (HV) circuit- 
breakers, the supporting structures of which are rigidly connected with the ground, and 
does not cover the seismic qualification of circuit-breakers in metal enclosed switchgear. 

The seismic qualification of the HV circuit-breakers shall take into account any auxiliary and 
control equipment which is mounted on the circuit-breaker structure. If the auxiliary and 
control equipment is mounted on a separate structure, it may be qualified independently. 

This standard is a guide providing procedures to seismically qualify HV alternating-current 
ground mounted circuit-breakers. It is mainly based on IEC 68-3-3, which in turn refers to 
IEC 68-1. IEC 68-2-6, IEC 68-2-47 and IEC 68-2-57. 



The seismic qualification of a circuit-breaker is only performed upon request. 

This standard specifies seismic severity levels and gives a choice of methods that can be 
applied to demonstrate the performance of HV circuit-breakers for which seismic qualifi- 
cation is required. 

2 Normative references 

The following normative documents contain provisions which, through reference in 
this text, constitute provisions of this International Standard. At the time of publication, 
the editions indicated were valid. All normative documents are subject to revision, and 
parties to agreements based on this International Standard are encouraged to investigate 
the possibility of applying the most recent editions of the normative documents indicated 
below. Members of IEC and ISO maintain registers of currently valid International 
Standards. 

IEC 50(441): 1984, International Electrotechnical Vocabulary (IEV), Chapter 441: Switch- 
gear, controlgear and fuses 

IEC 56: 1987, High-voltage alternating-current circuit-breakers 

IEC 68-1 : 1988, Environmental testing - Part 1: General and guidance 

IEC 68-2-6: 1982, Environmental testing - Part 2: Tests - Test Fc and guidance: 
Vibration (sinusoidal) 

IEC 68-2-47: 1982, Environmental testing - Part 2: Tests - Mounting of components, 
equipment and other articles for dynamic tests including shock (Ea), bump (Eb), vibration 
(Fc and Fd) and steady-state acceleration (Ga) and guidance 

IEC 68-2-57: 1989, Environmental testing - Part 2: Tests - Test Ff. Vibration - Time 
history method. 

IEC 68-3-3: 1991, Environmental testing - Part 3: Background information. Seismic test 
methods for equipment. 

1 



IS 14674 : 1999 
IEC 1166(1993) 

3 Definitions 

For definition of the terms used in this International Standard refer to IEC 68-3-3. 



4 Seismic qualification requirements 

The seismic qualification should demonstrate the circuit-breaker's ability to withstand 
seismic stress and to maintain its specified function, both during and after the seismic 
event. 

The most commonly used methods are: 

a) qualification by test; 

b) qualification by combined test and analysis. 

NOTE - Qualification by pure analysis is acceptable if sufficient information on physical parameters (e.g. 
damping coefficient) and on the functional behaviour of the circuit-breaker is available. 



5 Severities 

The severity levels shall be chosen from table 1 . 

Table 1 - Seismic qualification levels - horizontal severities 



Qualification 
level 


Required response 
spectrum 


Zero period 

acceleration (ZPA) 

m/s* 


AF5 
AF3 
AF2 


Figure 1 
Figure 2 
Figure 3 


5 
3 
2 



For vertical severities the direction factor (D) is 0,5 (see IEC 68-3-3). 

NOTES 

1 The required response spectrum of qualification level AF5 covers, in the range of predominant seismic 
frequency of 1 Hz to 35 Hz, the following response spectra: Endesa, Edelca, USA/NRC RG 1.60. Newmark 
Design Response Spectra (scaled to 5 m/s*), Nema (5 m/s 2 max. foundation acceleration), Oept. of Water & 
Power Los Angeles, San Diego SDG & E Imperial Substation. 

2 Information on the correlation between seismic qualification levels and different seismic scales is given 
in 8.2.4 of IEC 68-3-3. 

The selected qualification level should be in accordance with expected earthquakes at 
maximum ground motions for the location of installation. This level corresponds to S2 
earthquake (see 3.24 of IEC 68-3-3). 



IS 14674 : 1999 
IEC 1166(1993) 

6 Qualification by test 

6. 1 Introduction 

The test procedure for qualification of a circuit-breaker by test should be in accordance 
with clauses 1 1 to 15 of IEC 68-3-3. 

The tests shall be made at the ambient air temperature of the test location; this tem- 
perature shall be recorded in the test report. 

The qualification shall be carried out: 

- on a complete circuit-breaker when all poles are mounted on the same supporting 
structure; 

- on one pole in the case of a circuit-breaker with three separate poles; 

- on one column with its interrupters in the case of multibreak poles on separate 
supporting structures. 

NOTE - If a circuit-breaker cannot be tested with its supporting structure (e.g., due to its size), the 
dynamic contribution of the structure should be determined by analysts. 

The circuit-breaker shall be tested in the closed position except when the open position 
has been shown to be more critical during the vibration response investigation. 

6.2 Mounting 

General mounting requirements are given in IEC 68-2-47. The circuit-breaker shall be 
mounted as in service including dampers (if any). 

NOTE - For more detailed guidance in case of equipment normally used with vibration isolators (see A. 5, 
IEC 68-2-6). 

The horizontal orientation of the circuit-breaker should be in the direction of excitation 
acting along its two main orthogonal axes. 

Any fixtures or connections required only for testing should not affect the dynamic 
behaviour of the circuit-breaker. 

The method of mounting of the circuit-breaker shall be documented and shall include a 
description of any interposing fixtures and connections. 

6.3 External load 

Generally, electrical and environmental service loads cannot be simulated during the 
seismic test. This applies also to internal pressure of the circuit-breaker due to safety 
requirements of the test laboratory. 



NOTE - For combination of seismic and service loads, see clause 8. 

The circuit-breaker shall not be operated during the seismic tests; the control and auxiliary 
circuits shall be energized to monitor any chattering of relays, but they need not cause the 
circuit-breaker to operate. 



IS 14674 :1999 
IEC 1166(1993) 

6.4 Measurements 

Measurements should be performed in accordance with 5.2 of IEC 68-3-3, and should 
include: 

- vibration motion of the center of gravity (when applicable); 

- strains on critical elements (e.g. porcelains). 

6.5 Frequency range 

The frequency range shall be 0,5 Hz to 35 Hz. 

6.6 Test severity 

The test severity shall be chosen in accordance with clause 5. 

The recommended required response spectra are given in figures 1 to 3 for the different 
seismic qualification levels. The curves relate to 2 %, 5 %, 10 % and 20 % or more damp- 
ing ratio of the circuit-breaker. 

Spectra for different damping values can be obtained by linear interpolation. 

The time-history test method is to be preferred, since it more closely simulates actual 
conditions, particularly if the behaviour of the circuit-breaker under test is not linear. The 
test method should be in accordance with IEC 68-2-57. 

6.6.1 Parameters for sine-beat excitation 

Test frequencies shall cover the frequency range stated in 6.5 with 1/2 octave spacing. 
For each test frequency five sine-beats of five cycles each are applied. 



6.6.2 Parameters for time-history excitation 

The total duration of the time-history shall be about 30 s of which the strong part shall be 
not less than 6 s. 

6.7 Testing 

6.7.1 Test directions 

The test directions should be chosen according to 3.19 of IEC 68-3-3. 

In some cases the effect of the vertical acceleration results in negligible stresses and the 
vertical excitation may be omitted. 

6.7.2 Test sequence 

The test sequence shall be as follows: 

- functional checks before testing; 

- vibration response investigation (required to determine damping and/or for 
analysis); 

- seismic qualification test, and 

- functional checks after testing. 

4 



IS 14674 : 1999 
IEC 1166(1993) 



6.7.2.1 Functional checks 



Before and after the tests the following operating characteristics or settings shall be 
recorded or evaluated (when applicable) at the rated supply voltage and operating 
pressure: 

a) closing time; 

b) opening time; 

c) time spread between units of one pole; 

d) time spread between poles (if multipole tested); 

e) gas and/or liquid tightness; 

f) other important characteristics or settings as specified by the manufacturer. 

6.7.2.2 Vibration response investigation 

The vibration response investigation shall be carried out according to 10.1 and 14.2 of 
IEC 68-3-3 over the frequency range stated in 6.5. 

6.7.2.3 Seismic qualification test 

The test shall be performed by applying one of the procedures stated in flow chart A3 
(except test Fc) or flow chart A4 of annex A of IEC 68-3-3 depending on the test facilities. 

The test shall be performed once at the level chosen in clause 5. 

During the seismic test the following parameters shall be recorded: 

- strain of critical components such as post insulators and support structure; 

- deflection at terminal; 

- electrical continuity of the main circuit; 

- electrical continuity of the auxiliary and control circuit. 

7 Qualification by combined test and analysis 

7. 1 Introduction 

The method may be used: 

- to qualify a circuit-breaker which cannot be qualified by testing alone (e.g. because 
of its size and/or complexity); 

- to qualify a circuit-breaker already tested under different seismic conditions; 

- to qualify a circuit-breaker similar to a circuit-breaker already tested but which 
includes modifications influencing the dynamic behaviour (e.g. change in the length of 
insulators or in the mass of interrupters); 

- to qualify a circuit-breaker if its vibrational and functional data are known. 



IS 14674 : 1999 
IEC 1166(1993) 

7.2 Vibrational and functional data 

Vibrational data (damping, critical frequencies, stresses of critical elements as a function 
of input acceleration) for analysis can be obtained by: 

a) a dynamic test of a similar circuit-breaker; 

b) a dynamic test at reduced test level; 

c) determination of critical frequencies and damping by other tests such as free 
oscillation tests or low level excitation (see annex A). 

Functional data should be obtained from test performed on a similar circuit-breaker. 

7.3 Analysis 

The general procedure is: 

a) to establish, using experimental data stated in 7.2, a mathematical model of the 
circuit-breaker in order to assess its dynamic characteristics; 

b) to determine the response, in the frequency range stated in 6.5, using either of the 
methods described in the following subclauses, but other methods may be used if they 
are justified. 

7.3. 1 Acceleration time-history method of calculation 

When the time-history method is employed for seismic analysis, the ground motion 
acceleration time-histories shall comply with the RRS (see table 1). Two types of super- 
imposition may generally be applied depending on the complexity of the problem: 

a) separate calculation of the maximum responses due to each of the three 
components (x and y in the horizontal, and z in the vertical direction) of the earthquake 
motion. The effects of each single horizontal direction and the vertical direction shall 
be combined by taking the square root of the sum of the squares, i.e. (x 2 + z 2 )** and 
(y 2 + z*) V2 . The greater of these two values is used for dimensioning the circuit-breaker. 

b) simultaneous calculation of one of the horizontal directions and the vertical direction 
(x with z) and thereafter calculation of the other horizontal direction and the vertical 
direction (y with z). This means that after each time step of calculation all values 
(forces, stresses) are superimposed algebraically. The greater of these two values is 
used for dimensioning the circuit-breaker. 

7.3.2 Modal analysis using the required response spectrum (RRS) 

When the response spectra method is used for seismic analysis, the procedure of 
combining the stresses is hereinafter described for an orthogonal system of coordinates 
in the main axes of the circuit-breaker and with x and y in the horizontal and z jn the 
vertical direction. The maximum values of stresses in the circuit-breaker for each of 
the three directions x. y and z are obtained by super-imposing the stresses calculated for 
the various modal frequencies in each of these directions by taking the square root of 
the sum of the squares. The maximum values in the x and z direction - and in the y and z 
direction - are combined by taking the square root of the sum of the squares. The greater 
value of these two cases (x, z) or (y, z) is the dimensioning factor for the circuit-breaker. 



IS 14674 :1999 
lEC 1166(1993) 



7.3.3 Static coefficient analysis 



This method is adopted for rigid equipment. It may also be used for flexible equipment, 
as an alternate method of analysis; this allows a simpler technique in return for added 
conservatism. No determination of natural frequencies is made but, rather, the response 
spectrum of the circuit-breaker is assumed to be the peak of the required response 
spectrum at a conservative and justifiable value of damping. This response is then multi- 
plied by a static coefficient of 1 ,5 which has been established from experience to take into 
account the effects of both multifrequency excitation and multimode response. A lower 
static coefficient may be used if it can be shown to yield conservative results. 



The seismic forces on each part of the HV circuit-breaker are obtained by multiplying the 
values of the mass, concentrated at its center of gravity, and the acceleration. 

The resulting force should be distributed proportionally to the mass distribution. 
The stress analysis may then be completed as stated in 8.1. 

8 Evaluation of the seismic qualification 

8.1 Combination of stresses 

The seismic stresses determined by test or analysis shall be combined with other service 
loads to determine the total withstand capability of the circuit-breaker. 



The probability of an earthquake of the recommended seismic qualification level occurring 
during the life-time of the circuit-breaker is low, whilst the maximum seismic load in a 
natural earthquake would only occur if the circuit-breaker is excited at its critical 
frequencies with maximum acceleration. As this will last only a few seconds, a combi- 
nation of the utmost electrical and environmental service loads wouid lead to unrealistic 
conservatism. 

The following loads are considered to occur simultaneously, if not otherwise specified: 



- internal pressure; 

- static terminal load. 

NOTE - See the values given in 6.101.6.1 of IEC 56. Multiply the static terminal load by 0,7, to take into 
account a wind velocity of only 10 m/s on connected conductors. 

- wind force of 10 m/s on the circuit-breaker; 

- seismic forces. 

The stresses due to the combination of these loads shall be equal to or less than 
the guaranteed minimum bending stress of each of the considered critical elements (e.g. 
support insulator). 

The combination of loads can be done by static analysis (see figure 4). 



IS 14674 : 1999 
IEC 1166(1993) 

8.2 Acceptance criteria of the seismic simulation 

The seismic simulation waveforms shall produce a test response spectrum which 
envelopes the required response spectrum (calculated at the same damping ratio) and 
have a peak acceleration equal to or greater than the zero period acceleration. 



8.3 Functional evaluation of the test results 

Functional results are normally obtained only by dynamic tests. These results may be 
extrapolated to obtain qualification by combination of tests and analysis. In particular: 

a) the main contacts shall remain in position during the seismic test; 

b) chatter of relays shall not cause the circuit-breaker to operate; 

C) chatter of relays shall not provide wrong information of the status of the circuit- 
breaker (position, alarm signals). 

NOTE - Normally, chatter of relays during less than 5 ms is considered to be acceptable. 

d) resetting of monitoring equipment is considered to be acceptable if the overall 
performance of the circuit-breaker is not affected; 

e) no significant change should occur in functional checks recordings at the end of the 
test sequence compared with the initial ones (see 6.7.2.1). 

9 Documentation 

9.1 Information for seismic qualification 

The following information is required for either analysis or testing of the circuit-breaker: 

1) Severity (clause 5). 

2) Details of mounting (6.2). 

3) Number and relative position of testing axes. 

9.2 Test report 

The test report shall contain: 

1) Circuit-breaker identification file including mounting details. 

2) Information for seismic qualification. 

3) Test facility: 

a) location; 

b) test equipment description and calibration. 

4) Test method and procedures. 

5) Test data including functional data (see 6.7.2.1 and 7.2). 

6) Results and conclusions 

7) Approved signature and date. 

9.3 Analysis report 

Analysis, which is included as a proof of performance, should have a step-by-step pre- 
sentation. 

8 



IS 14674 : 199S 
IEC 1166(1693 




0,1 0.2 0.5 1 2 5 10 20 

Frequency (Hi) 



SO 100 



Frequency 
Hz 


Amplitude 
m/s* 


Damping 
2% 


Damping 
5% 


Damping 
10% 


Damping 
20% 
and more 


0,5 
1,0 
2.4 
9,0 
20.0 
25,0 


4,3 
8,5 
14,0 
14,0 
7,5 
5,0 


2.9 
5,2 
8.7 
8.7 
7.0 
5.0 


2.1 
4.3 
6.4 
7.3 
6,4 
5.0 


1.8 
3,2 
5,2 
6,1 
5,2 
5,0 



NOTE • According to IEC 68-3-3, the value of g is rounded up to the nearest unity, that is 10 m/s 2 . 

Figure 1 - RRS for ground mounted equipment. 

Qualification level: AF5: ZPA - 5 m/s 2 (0.5 fl) 



IS 14674 : 1999 
IEC 1166(1993) 



1 000 




Frequency 
Hz 


Amplitude 
m/s 2 


Damping 
2% 


Damping 
5% 


Damping 
10% 


Damping 
20% 
and more 


0,5 
1.0 
2,4 
9.0 
20,0 
25,0 


2.6 
5.1 
8.5 
8.5 
4.5 
3,0 


1.8 
3,2 
5,1 
5,1 
4,1 
3.0 


1.4 
2,3 
3.8 
4,2 
3.8 
3.0 


0.8 
1,6 
2,9 
3,6 
3,1 
3.0 



NOTE - According to IEC 68-3-3, the value of g is rounded up to the nearest unity, that is 10 m/s*. 

Figure 2 - rrs for ground mounted equipment. 

■Qualification level: AF3: ZPA '- 3 m/s 2 (0,3 g) 



10 



IS 14674 : 1999 
IEC 1166(1993) 



1 000 




0,1 0,2 



0.5 



2 5 10 20 

Frequency (Hz) 



50 100 



Frequency 
Hz 


Amplitude 
m/s* 


Damping 
2% 


Damping 
5% 


Damping 
10% 


Damping 

20% 

et plus / and more 


0,5 
1.0 
2.4 
9.0 
10,0 
25.0 


1.7 
3,4 
5,6 
5,6 
5.0 
2.0 


1.2 
2.2 
3.4 
3.4 
2.8 
2.0 


0,8 
1.7 
2,6 
2,8 
2.6 
2.0 


0,6 
1,2 
2.0 
2,4 
2.4 
2.0 



NOTE • According to IEC 68-3-3, the value of g is rounded up to the nearest unity, that is 10 m/s 2 -. 

Figure 3 - RRS for ground mounted equipment. 

Qualification level AF2: ZPA « 2 m/s 2 (0,2 g) 



11 



IS 14674 : 1999 
IEC 1166(1993) 



A 



y A 



t 



3=33=03 



Supporting insulatorstress at A-A 



max 



<r-» 


> 


* ^ 






N 


\ 
\ 


\ 






\ 


\ 


n -x 




\ 


\ 




\ 


\ 
\ 


\ 


<r-» 


\ 
\ 


\ 
\ 


t 




\ * 


\ 


t 




\» 




• 


^ 


t 

W 


*L_ 


1 

— J 



p W 8 

max 



Stresses due at: 

- p internal pressure 

- w wind pressure on the circuit breaker 

- F static terminal load 

- s seismic force 

- F maximum permissible bending stress 



Figure 4 - Example for combination of stresses 



12 



IS 14674 :1999 
IEC 1166(1993) 



100 
90 
80 
70 
60 

50 

40 

30 



20 



10 
9 
8 

7 
6 











m^hm*/ww?m7. 



i^M ^mmm. 






I ;..■■■ .- / .- .- .- ,- ■ i .- : i j ~- VyrzTTr^zz 







1 X^^^^M^^^^^^M^^j^^^i W\ 




























n + li 



__n = 7_| 



L'.. ._&_ 



::*_"Ur: Typical case of free oscillations 



...:,.i Note: "n" designs the number of cyc les gf 

— I— j— — '— - 



S 



— Y^/Y, values TJf; 




0.4 



0,3 



0.2 



0.1 



Figure 5 - Graph for determining the clamping ratio 



13 



IS 14674 :1999 
IEC 1166(1993) 

Annex A 

(normative) 

Characterization of the equipment 

A.1 Low level excitation 

The method combines testing and analysis and utilizes the application of excitation at 
points in the circuit-breaker with low level excitation for response determination. 

A. 1.1 Test method 

With the circuit-breaker mounted to simulate the recommended service mounting condi- 
tions, a number of portable exciters are attached at the points on the circuit-breaker which 
will best excite its various modes of vibration. 

The data obtained from the monitoring instruments placed on the circuit-breaker can be 
used to analyze the circuit-breaker's seismic performance. 

A. 1.2 Analysis 

The frequency response functions obtained from the test can be used to determine 
the modal frequencies and damping which may be used in a dynamic analysis of the 
circuit-breaker. This method provides a greater degree of certainty in analysis since 
the analytical model can be refined to reflect the measured natural frequencies and experi- 
mental damping ratios can be used. 

A. 1.3 Qualification 

This method can adequately qualify the circuit-breaker in either of two ways, namely: 

- the circuit-breaker can be excited to a level at least equal to the expected response 
from a design earthquake, using analysis to justify the excitation; 

- the test data on modal frequencies can be used in a mathematical model to verify 
performance. 

The first method is based upon the equivalence between the effects due to the base 
excitation (earthquake) and the concentrated force excitation. The equivalence is obtained 
if the circuit-breaker responses give the same relative displacements in the two cases. 



A.2 Free oscillation test 

A.2.1 Natural frequency determination 

To determine the natural frequency (first vibration mode) of the circuit-breaker, the circuit- 
breaker, fully furnished for service, shall be fixed to a rigid foundation by the means 
provided for in its design. A tensile force, of value not less than one-third of the weight of 
the oscillating equipment, shall be applied along the direction of maximum probable ampli- 
tude, in the vicinity of the center of gravity of the circuit-breaker. The oscillations of the 
circuit-breaker shall be recorded when this force is suddenly released. 

14 



IS 14674 : 1999 
IEC 1166(1993) 



A.2.2 Damping ratio determination 



To determine the clamping ratio of the circuit-breaker, the same test may be used but, in 
this case, the recording of the oscillations shall be made with suitable sensitivity and 
accuracy to determine the decrement of the oscillations as a function of time. The equi- 
valent damping ratio is determined using the monogram in figure 5, from the sequence of 
peaks in the recorded wave, in that range of the record in which the logarithmic decrement 
appears most clear. 

A.2.3 Special cases in the natural frequency and damping ratio determination 



When the circuit-breaker consists of different elements, each one susceptible to vibration, 
the tests in A.2.1 and A.2.2 shall be made by applying tensile force around the centre of 
gravity of each of the several masses subject to vibration and simultaneously recording 
the oscillation of those points corresponding to the greatest amplitude, while attempting 
to detect all the modes of oscillation in the arrangement. In such cases, it is possible that 
the record of oscillations in one element is influenced by the oscillations of some 
other element with a nearby frequency, in which case the determination shall be made as 
described in the sketch of the top of figure 5. 



15 



(Continued from second cover) 



International Standard 



Corresponding 
Indian Standard 

IS 9001 (Part 12): 1979 



Degree of 
Equivalence 

Equivalent 



I EC 68-2-47: 1982 
Environmental testing — Part 2 : 
Tests — Mounting of components, 
equipment and other articles for 
dynamic tests including shock (Ea), 
bump (Eb), vibration (Fc and Fd) 
and steady state acceleration 
(Ga) and guidance 

I EC 68-2-57 : 1989 Environmental No ISS Exists — 

testing — Part 2 : Tests — Test Ff. 
Vibration — Time history method 

IEC 68-3-3: 1991 Environmental No ISS Exists — 

testing — Part 3 : Background 
information. Seismic test 
methods for equipment 

Only the English language text in the International Standard has been retained while adopting it in this 
Indian Standard. 

For the purpose of deciding whether a particular requirement of this standard is complied with, the final 
value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance 
with IS 2 : 1960 'Rules for rounding off numerical values (revised)'. The number of significant places 
retained in the rounded off value should be the same as that of the specified value in this standard. 



Bureau of Indian Standards 

BIS is a statutory institution established under the Bureau of Indian Standards Act, 1986 to 
promote harmonious development of the activities of standardization, marking and quality cer- 
tification of goods and attending to connected matters in the country. 

Copyright 

BIS has the copyright of all its publications. No part of these publications may be reproduced in 
any form without the prior permission in writing of BIS. This does not preclude the free use, in 
the course of implementing the standard, of necessary details, such as symbols and sizes, 
type or grade designations. Enquiries relating to copyright be addressed to the Director (Pub- 
lications), BIS. 

Review of Indian Standards 

Amendments are issued to standards as the need arises on the basis of comments. Standards 
are also reviewed periodically; a standard along with amendments is reaffirmed when such 
review indicates that no changes are needed; if the review indicates that changes are needed, 
it is taken up for revision. Users of Indian Standards should ascertain that they are in posses- 
sion of the latest amendments or edition by referring to the latest issue of 'BIS Handbook' and 
'Standards: Monthly Additions'. 

This Indian Standard has been developed from Doc : No. ET 08 (5012). 



Amendments Issued Since Publication 



Amend No. 



Date of Issue 



Text Affected 



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